In a number of applications of food- and healthcare industry use free glucose and fructose—that is glucose and fructose as monosaccharides—as ingredient or raw material is preferred to using sucrose. However free glucose and even more free fructose are at present prized substances, much more expensive than sucrose. For example free fructose is quite appreciated as sweetening agent in almost any foodstuff, in particular drinks, bakery products and jams, since it is the known sweetest naturally occurring carbohydrate. Free fructose is quite appreciated by diabetics since it raises glycaemia less than sucrose. In several cases also free glucose is preferred to sucrose as sweetener in the food industry, medicine and dietetics.
At present several processes are known for obtaining free glucose and fructose in industrial quantities. For example it is known to obtain fructose by separating invert sugar through chromatographic processes, as described for example in the U.S. Pat. Nos. 6,325,940 and 3,416,961. The invert sugar is obtained from beets by splitting sucrose in glucose and fructose with a chemical process and, according to current norms, in several countries may be considered and labelled neither “natural sugar” nor “all natural”.
It is also currently known obtaining free fructose or glucose through the enzymatic conversion of a part of the glucose contained in the so-called “high-fructose-corn-syrup” (HFCS). However such glucose and fructose may be considered and labelled neither “natural sugars” nor “OGM free” as well. Furthermore free glucose and fructose obtained in massive quantities with known methods have a relatively low purity: for example current european norms require that, in order to be labelled as “pure fructose”, a liquid fructose solution have a solid content of at least 95% wt fructose, while crystal fructose have a solid content of 99.5% wt fructose. On the contrary free glucose and fructose obtained with current mass-production processes often hardly achieve such degrees of purity, or achieve them at too high costs.
Therefore at present need is felt for having available massive quantities of free fructose and glucose—that is, as monosaccharides—at high purity and at a relatively low costs.
At present consumers and legislators appreciate more and more the so called “natural foods”, “natural products” or “biological products”, that is foods and ingredients obtained with processes as much direct and natural as possible, and having a taste as natural as possible. These demands are felt in the production of sweeteners and wine as well.
Grapes and fruits in general are known to internally contain free glucose and fructose and smaller amounts of other natural saccharides, referred to as “minor sugars” in the present description. Therefore theoretically speaking fruits could seem an immediate source of natural fructose and glucose. However until now no satisfying processes are known for extracting free glucose and fructose from fruits in industrial quantities at acceptable costs. What it has long been known is extracting from grapes an aqueous mixture containing water, fructose and glucose, and known as rectified concentrated must.
Liquid rectified concentrated must is used nowadays in the food industry as sweetener in yogurts, jams and juices and allows to use the indication “with no added sugars”. Liquid rectified concentrated must is also used in wine industry for raising the proof spirit of fermenting must. It is also known to process liquid rectified concentrated must for producing rectified concentrated must in crystalline or powder form.
In particular, the Italian patent application RM99A000662 and the corresponding european application EP1096006 describe a process in which the liquid rectified concentrated must is initially concentrated to a concentration of 82° brix and then mixed with neutral 96° ethyl alcohol, in the proportion of 1:1 (i.e. 50% ethyl alcohol and 50% liquid rectified concentrated must).
The mixture of ethyl alcohol and liquid rectified concentrated must is stirred to enable the ethyl alcohol to extract the water contained within the sugars.
This operation results in separation into a lower layer of pasty grape sugar and an upper layer of ethyl alcohol and water.
The mixture of water and ethyl alcohol is then removed and distilled (to recover the ethyl alcohol) while the pasty matter is kept for at least 15 days at a temperature of −⅚° C. for crystal formation.
After the time required for crystal formation (at least 15 days) the crystals are centrifuged, washed and maintained in a dryer to obtain the final product. The final product obtained does not present a true crystalline or powder structure, but instead is in the form of a gelatinous mass, consisting of: glucose and fructose sugars (and other minimal quantities—about 1% wt or less—of substances present in the grapes defined as “non-sugar”), ethyl alcohol and water.
In this respect, the ethyl alcohol removes only part of the water, the final drying not being able to eliminate the remainder of the water, which therefore remains incorporated in the interior of the gelatinous mass without being able to emerge from it.
The gelatinous mass is also unstable in air and difficult to work.
Another drawback is the high cost of the ethyl alcohol, both at the purchase stage and in its recovery; this evidently affects the cost of the final product.
The crystal maturing time is very lengthy and usually varies considerably depending on the particular conditions under which it takes place, this leading to difficult industrialization of the process.
In addition, crystal washing inevitably modifies the fructose/glucose weight ratio because of the greater water solubility of fructose compared with glucose.
To rebalance this ratio an attempt has been made to enrich the starting solution concentrated to 82° brix with the fructose recovered from the wash water and reconcentrated.
However the finished product obtained is unsatisfactory in terms of its dryness, taste and smell.
A scope of the present invention is providing a process and a plant for obtaining and separating concentrated natural monosaccharides in industrial amounts, in particular concentrated glucose and fructose, with a higher yield and at lower costs than with known processes or plants.